1. Field of the Invention
The present invention relates to resin concrete compositions from which molded articles having no cracks can be obtained with little shrinkage without using a shrinkage reducing agent as well as being excellent in flowability and the hardened articles thereof having high strengths even with reduced resin contents. The present invention also relates to molded articles of the resin concrete compositions.
2. Description of Related Art
Resin concrete compositions containing an unsaturated polyester resin composition which incorporate an unsaturated polyester and a polymerizable unsaturated monomer, an aggregate, and a filler have been known, and industrially, resin concrete compositions have been used for products related to water supply and sewers, such as manholes, pipes, and drainage basins, for repairing cracks in cement concrete, for molded articles for landscaping such as garden lanterns, and for the like. Conventional resin concretes, particularly those having no coarse aggregate and having a relatively high resin content such as 15 to 20%, normally incorporate a shrinkage reducing agent consisting of a thermoplastic resin such as polystyrene and polyvinyl acetate in order to avoid cracking due to shrinkage during hardening in a molding process, and clinging to the mold.
However, since a shrinkage reducing agent itself cannot be hardened, problems such as the following have occurred:
The obtained molded article has a reduced strength. PA1 The surface of the molded article becomes sticky. PA1 The molded products are irregular in their dimensions and strength because of differences in shrinkage reducing effect due to different temperatures of the exothermic reaction during hardening, caused by variations in seasons, atmospheric temperatures, temperatures in the curing oven, or the like. PA1 With a certain type of shrinkage reducing agent, the appearance of the molded product deteriorates since the shrinkage reducing agent is poorly compatible with the unsaturated polyester resin, and therefore when they are combined to make a resin concrete, the flowability and the ease of degassing are degraded. PA1 The necessity of increasing the resin content results in an increase in the cost. PA1 (1) A one-step synthetic process in which the modification occurs concurrently by putting the acid, the glycol, and dicyclopentadiene in a vessel at the same time and condensing them. PA1 (2) A two-step synthetic process in which the acid and the glycol are condensed, and in the middle of the condensation dicyclopentadiene is added thereto to let the modification proceed. PA1 (3) A process in which an addition reaction is allowed to occur between an acid anhydride and dicyclopentadiene in the presence of water to produce a monoester, and thereafter the glycol and the acid are added thereto and the reaction is allowed to occur. PA1 A cast molding method, in which the resin concrete composition is poured into a mold, and hardened at a normal or heated temperature. PA1 A centrifugal molding method, in which the resin concrete composition is poured into a cylindrical mold, thereafter the mold is rotated, a uniform thickness of the resin concrete composition is formed by the centrifugal force of the rotation, and the resin concrete composition is hardened at a normal or heated temperature. PA1 A compression molding method, in which the resin concrete composition is poured into matching molds, thereafter the molds are compressed by a molding machine, and the resin concrete composition is hardened at a normal or heated temperature.
In addition, use of dicyclopentadiene-modified unsaturated polyester as the unsaturated polyester in the resin concrete has been known, for example, as disclosed in International Publication No. WO87/04442 and Japanese Unexamined Patent Application, First Publication (Kokai) No. Hei 4-149050. However, there were problems in that the strengths of the resin concrete molded articles were low, and the cracking resistance was insufficient.